Effect of sodicity and zinc on soil solution chemistry of manganese under submerged conditions

Abstract

SummaryIn a greenhouse experiment, the effect of soil sodicity (exchangeable Na percentage 3, 10, 20, 40 and 60) and Zn (0 and 10 mg Zn/kg soil) on soil solution chemistry of Mn was investigated under submerged conditions. Calculated amounts of NaHCO3 were added to Typic Ustifluvent sandy loam soil to obtain required sodicity levels. The soil solutions collected under the atmosphere of N2 gas by gravity were analysed for pH, pE, EC and Mn. Soil submergence decreased pH and pE, and increased Mn concentrations in all the treatments. Maximum Mn concentration was obtained at 14-day submergence. Increasing sodicity levels increased soil solution pH and decreased Mn concentrations. A significant negative correlation (r = -0·74**) was observed between soil solution Mn and pH. Despite large variations in pH, pE, ionic strength and Mn concentration in soil solution, the values of expressions: pH+½log Mn2+ + ½log Pco2 and pMn+2pOH were fairly constant and close to the theoretical values of 4·4 and 17·2 respectively, indicating that the MnCO3-Mn2+ system regulated the solubility of Mn2+ in the sodic soils. Addition of ZnSO4 did not have appreciable effects on the soil solution pH, Mn and solid phases of Mn.